A method and an arrangement of the above kind for checking the operability of a tank-venting system are disclosed in U.S. patent application Ser. No. 08/900,335, filed on Jul. 25, 1997. Such a diagnostic method can only supply reliable diagnostic results when the vehicle is at standstill. This is so because, for a moving vehicle, the ambient pressure can change (for example, when traveling in mountainous country) and this and, for example, fuel sloshing in the tank constitute disturbances which are too great.
A reliable leakage diagnosis can therefore only be executed for a vehicle at standstill. However, it cannot be excluded here that the vehicle has just been tanked full and a leak is signaled which is not present.
A method is disclosed in U.S. patent application Ser. No. 08/722,682, filed on Sep. 30, 1996, wherein one an conclude the presence of a tanking operation based on a pressure trace characteristic of a tanking operation.
It is problematic with respect to this method that a pressure sensor must be present in the tank which detects the pressure trace in the tank.